The present invention relates to a communication method adopting a multi-carrier modulation-demodulation mode. More, particularly this invention relates to a communication method capable of realizing data communication using an existing power line by a DMT (Discrete Multi Tone) modulation-demodulation mode or an OFDM (Orthogonal Frequency Division Multiplex) modulation-demodulation mode, and to a communication device capable of realizing the communication method. It is noted, however, that the present invention should not be limited to a communication device for holding communication using a power line by the DMT modulation-demodulation mode. The present invention is applicable to all communication devices holding wire communication and radio communication through an ordinary communication line by a multi-carrier modulation-demodulation mode or a single-carrier modulation-demodulation mode.
A conventional communication method will be described hereinafter. In recent years, attention is being paid to xe2x80x9ca power line modemxe2x80x9d for holding communication using an existing power line without adding a new communication line so as to cut cost and to make an effective use of existing facilities. This power line modem conducts various processings including the control of electrical products inside or outside of houses, in buildings, factories, shops and the like connected by a power line, data communication and the like by establishing a network.
As a power line modem of this type, one using an SS (Spread Spectrum) mode is currently proposed. This mode has disadvantageous if the mode is used. For example, since spectra are emitted to range all over a given band, it is difficult that this SS mode and other communication modes coexist. In this mode, transfer rate for a used band is low. Further, if an existing power line which is not mainly intended at data communication such as a power line modem stated above is used for data communication, various equipment connected to the line so as to feed power to the equipment become noise sources. Thus, measures against noise should be taken.
Considering these disadvantages and from the viewpoint of high noise resistance, communication methods adopting a multi-carrier communication mode capable of holding communication wherein the same data is put on a plurality of frequency bands and communication using frequency bands less influenced by noise, are gradually proposed. In this multi-carrier communication mode, to-be-transmitted information data is divided and subjected to a primary modulation such as frequency conversion at a transmission (modulation) side and then a secondary modulation using IFFT (inverse fast Fourier transformation), i.e., multi-carrier modulation is conducted, thereby spreading the information data which has been subjected to the primary modulation to multiple carriers. A reception (or demodulation) side which has received data on the respective tones which data spread to the multiple carriers, performs an opposite processing to that of the transmission side, thereby demodulating the received data to original information data.
According to the communication method using the conventional multi-carrier communication mode as described above, the modulation mode for the primary modulation cannot be selectively changed. Due to this, in a communication environment in which noise has great influence, communication quality is enhanced by putting the same data on a plurality of carriers or moving tones. For example, if the influence of noise is widespread, these measures cannot disadvantageously suppress the influence of noise and communication quality equal to or higher than a certain level cannot be disadvantageously maintained.
In the environments of power line communication, in-vehicle communication by means of a navigator equipment, a computer, an ITS communication device or other electronic equipment installed to an automobile or the like and in-train communication for electric railcars and the like, the level of noise from the other equipment such as inverter noise is high, wide spread and changeable. As a result, it is quite difficult to maintain communication quality equal to or higher than a certain level. Thus, anti-noise measures other than the above-stated measures are further demanded.
It is an object of the present invention to provide a communication method capable of constantly maintaining high level, fixed communication quality without deteriorating characteristics even in communication environments greatly influenced by noise, and a communication device capable of realizing the communication method.
The communication method according to one aspect of this invention adopts a multi-carrier modulation-demodulation mode as a communication mode for data communication to be held among a plurality of communication devices connected to a transmission line and selects tones less influenced by noise and thereby operating to maintain fixed communication quality. The communication method comprises a first tone set movement step of monitoring the transmission line while the communication is held in a steady state, and judging that the communication quality cannot be maintained if there are no tones securing a specific standard, and moving a tone set by a predetermined method; a second tone set movement step of judging that the certain communication quality can be maintained and not moving the tone set if the number of tones securing the specific standard is equal to or higher than a predetermined number, and moving the tone set by the predetermined method if the number of the tones securing the specific standard is less than the predetermined number and it is judged that the communication quality can be maintained by moving the tone set in a same tone group; and a tone group movement step of moving the tone group by a predetermined method if it is judged that the communication quality cannot be maintained even by moving the tone set in the same tone group.
The above-mentioned communication method preferably further comprises a change step of recognizing a present state by monitoring a fixed tone set to which a position of a tone set currently used for communication is written, at a time of turning on power, and changing the tone set to the present state; and a frame transmission step of transmitting a frame using a tone set which has been set during initialization and waiting for a response from other communication devices if the fixed tone set cannot be received.
The above-mentioned communication method preferably further comprises a primary modulation mode selection step of selecting one of primary modulation modes having different noise resistances based on a predetermined standard if it is judged that the communication quality cannot be maintained even by making the primary modulation modes having different noise resistances selectable, executing movement of the tone set in the same tone group and executing movement of the tone group.
The above-mentioned communication method preferably further comprises a change step of recognizing a present state by monitoring a fixed tone set to which a position of a tone set currently used for communication and a primary modulation mode are written, at a time of turning on power, and changing the tone set to the present state; and a frame transmission step of transmitting a frame using a tone set which has been set during initialization and waiting for a response from other communication devices if the fixed tone set cannot be received.
In the above-mentioned communication method, in the primary modulation mode selection step, a DQPSK mode, a DBPSK mode and a BPSK+time diversity mode are selected as the primary modulation mode in this order.
In the above-mentioned communication method, in the fist tone set movement step, the position of the tone set in the same tone group is gradually moved from either a low frequency side or a high frequency side.
In the above-mentioned communication method, in the second tone set movement step, the position of the tone set is moved so that a good tone is located at a center based on a result of checking whether the specific standard can be secured.
In the above-mentioned communication method, in the tone group movement step, the tone group is moved in an order of tone group numbers.
In the above-mentioned communication method, characterized in that if a frame is received from a newly connected communication device, information on a tone set currently used for communication is put on a fixed tone set and transmitted.
The communication device according to one aspect of this invention adopts a multi-carrier modulation-demodulation mode as a communication mode for data communication to be held among a plurality of communication devices connected to a transmission line and selects tones less influenced by noise and to thereby maintain fixed communication quality. Furthermore, the transmission line is monitored while the communication is held in a steady state, it is judged that the communication quality cannot be maintained if there are no tones securing a specific standard, and a tone set is moved by a predetermined method; it is judged that the certain communication quality can be maintained and the tone set is not moved if the number of tones securing the specific standard is equal to or higher than a predetermined number, and the tone set is moved by the predetermined method if the number of the tones securing the specific standard is less than the predetermined number and it is judged that the communication quality can be maintained by moving the tone set in a same tone group; and the tone group is moved by a predetermined method if it is judged that the communication quality cannot be maintained even by moving the tone set in the same tone group.
In the above-mentioned communication device, a present state is recognized by monitoring a fixed tone set to which a position of a tone set currently used for communication is written at a time of turning on power, and the tone set is changed to the present state; and a frame is transmitted using a tone set which has been set during initialization and a response from other communication devices is awaited if the fixed tone set cannot be received.
In the above-mentioned communication device, one of primary modulation modes having different noise resistances is selected based on a predetermined standard if it is judged that the communication quality cannot be maintained even by making the primary modulation modes having different noise resistances selectable, executing movement of the tone set in the same tone group and movement of the tone group.
In the above-mentioned communication device, a present state is recognized by monitoring a fixed tone set to which a position of a tone set currently used for communication and a primary modulation mode are written, at a time of turning on power, and the tone set is changed to the present state; and a frame is transmitted using a tone set which has been set during initialization and a response from other communication devices is awaited if the fixed tone set cannot be received.